Of course! If you're a teenage nerd, everyone says you're dumb. Well, there you begin to think that you are stupid in life and once again it is better not to blur anything out in public. And when you grow up, everyone says not that you are stupid but that you are an introvert.
This is hardly possible. First, brain retardation occurs due to poor development of the brain itself, starting in childhood. If you or your parents did not think about this, then naturally you will think more slowly and the like. Either this is the initial stage of some kind of illness (but I definitely don't understand this anymore)
Whether you are an introvert or not depends on your character. I'm not talking about how you were raised, but about how you were born. From birth, everyone has a certain direction of the psyche: outward in extroverts, inward in introverts. Let me explain with an example. Let's say you are offered a book. The first thing an introvert does is think about whether he needs this book or not. (thinks inside) If he has a family, then he thinks: does one of them need a book, nothing more. And the extrovert immediately thinks (outward) both about himself and about those around him: not only about his family, but also about other relatives, about friends, and even about neighbors! Of course, over time, people can adapt, but not completely. An introvert will not become an extrovert, and vice versa.
Also, if you thought introverts were more selfish, then it seemed to you. Selfishness does not depend on it.